You can install MSDTC before or after SQL Server installation. If your Windows cluster is going to host a single SQL Server instance you can set up MSDTC resource to use the same SQL Server cluster group. If you want to keep MSDTC isolated or you are going to use multiple SQL Server instances and want to use a single MSDTC, you can created its own cluster group.
If your SQL Server client application do not use distributed transactions do not install it.
MSDTC Recommendations on SQL Failover Cluster